268 THE SKELETON. 



digital extremity, and, running backward, converge to meet together a little 

 behind the centre of the bone and form a ridge which runs along the rest of the 

 dorsal surface to the carpal extremity. This ridge separates two lateral, sloping 

 surfaces for the attachment of the Dorsal interossei muscles. 1 To the tubercles 

 on the digital extremities are attached the lateral ligaments of the metacarpo- 

 phalangeal joints. 



The carpal extremity, or base, is of a cuboidal form, and broader behind than 

 in front; it articulates above with the carpus, and on each side with the adjoining 

 metacarpal bones ; its dorsal and palmar surfaces are rough, for the attachment of 

 tendons and ligaments. 



The digital extremity, or head, presents an oblong surface, flattened at each 

 side ; it articulates with the proximal phalanx ; it is broader and extends farther 

 forward in front than behind, and is longer in the antero-posterior than in the 

 transverse diameter. On either side of the head is a tubercle for the attachment 

 of the lateral ligament of the metacarpo-phalangeal joint. The posterior surface, 

 broad and flat, supports the Extensor tendons ; the anterior surface is grooved in 

 the middle line for the passage of the Flexor tendons, and marked on each side by 

 an articular eminence continuous with the terminal articular surface. 



Peculiar Characters of the Metacarpal Bones. 



The metacarpal bone of the thumb is shorter and wider than the rest, diverges 

 to a greater degree from the carpus, and its palmar surface is directed inward 

 toward the palm. The shaft is flattened and broad on its dorsal aspect, and 

 does not present the ridge which is found on the other metacarpal bones; it is 

 concave from before backward on its palmar surface. The carpal extremity, 

 or base, presents a concavo-convex surface, for articulation with the trapezium ; 

 it has no lateral facets. The digital extremity is less convex than that of the 

 other metacarpal bones, broader from side to side than from before backward, and 

 terminates anteriorly in a small articular, eminence on each side, over which play 

 two sesamoid bones. 



The side to which this bone belongs may be known by observing the little 

 prominence which is situated on the outer or radial side of its posterior surface just 

 above the base, for the tendon of the Extensor ossis metacarpi pollicis. If the 

 bone is held with the palmar surface upward and the base toward the student, 

 the prominence will point to the side to which the bone belongs. Another means 

 by which the side to which the bone belongs may be ascertained is by holding it 

 in the position it occupies in the hand, with the carpal extremity upward and the 

 dorsal surface backAvai*d ; the narrower, radial border will point to the side to 

 which it belongs. 



The metacarpal bone of the index finger is the longest and its base the largest 

 of the other four. Its carpal extremity is prolonged upward and inward, forming 

 a prominent ridge. The dorsal and palmar surfaces of this extremity are rough, 

 for the attachment of tendons and ligaments. It presents four articular facets: 

 three on the upper aspect of the base : the middle one of the three is the largest, 

 concave from side to side, convex from before backward, for articulation with the 

 trapezoid ; the external one is a small, flat, quadrilateral facet, for articulation with 

 the trapezium ; the internal one on the summit of the ridge is long and narrow, 

 for articulation with the os magnum. The fourth facet is on the inner or ulnar 

 side of the extremity of the bone, and is for articulation with the third metacarpal 

 bone. 



The side to which this bone belongs is indicated by the absence of the lateral 

 facet on the outer (radial) side of its base, so that if the bone is placed with its 

 base toward the student and the palmar surface upward, the side on which there 

 is no lateral facet will be that to Avhich it belongs. 



1 By these sloping surfaces the metacarpal bones of the hand may be at once differentiated from 

 those of the ioot. 



